The present invention relates to a boom, or lance, for applying vitreous coatings, such as glass, or enamel, to the internal surface of a heated horizontally rotating, cylindrical article, such as a vessel, or tank to form a thin, uniform, continuous, fused coating thereon.
Glass lined vessels have found widespread use in numerous industries, particularly those industries which require the storage or reaction of corrosive materials. Such vessels find use in extraction, suspension and distillation processes. The glass lining facilitates the use of the vessels under numerous adverse temperature and corrosive corrosive conditions.
Various methods and apparatus have been proposed to apply internal coatings to tubular articles such as reactors. Typical examples of these are: U.S. Pat. Nos. 3,351,289; 3,484,266; 3,827,633; 3,876,190, and 4,150,176. Generally booms, or lances, consisting of an elongated tubular member are utilized. Coating material is fed in one end, transported through the tube portion, to and through, a distribution means located in the furnace end of the boom. The article being coated is typically heated and rotated, while the coating material is distributed therein. As the boom moves through the length of the rotating article the interior of the article is coated.
In coating vitreous material such as glass on steel, it is imperative that an integral coating be obtained. Small defects such as, areas not coated completely, pinholes, blisters, or abrasions, result in rapid deterioration of the substrate adjoining the defective area especially when the coated article is subjected to corrosive conditions.
The prior art methods using a particulate coating material, such as glass, typically utilize it in a carrier such as water. The mixture is applied to the interior of the article being coated. After the mixture is applied, the article is dried to remove the carrier and subsequently fired to obtain the finished coated article. If defects in the coating are found after cooling the process is repeated. Most prior art processes, such as U.S. Pat. No. 3,484,266, noted above, initially distribute particulate materials on the vessel surface and subsequently in a separate step fuse the particles to obtain the finished coating. The reason a subsequent and completely separate firing step is required, is that mechanical apparatus, such as, glass feeding and dispensing mechanisms, do not reliably operate at glass firing temperatures. Typically, such temperatures range between about 1500.degree. and about 1700.degree. F. In addition, the particulate feed material frequently becomes tacky at such high temperatures leading to uneven distribution and a faulty coating.
U.S. Pat. No. 3,788,874 teaches a method of glass coating by maintaining the article to be coated at a temperature at least as high as the fusion point of the glass, while depositing glass particles on the article at a rate no greater than the rate at which the particles fuse to the article. While this method has many advantages it has not been widely utilized on a commercial basis because equipment to facilitate the commercial use of the method has not been developed. The present invention provides a boom by which the method of the U.S. Pat. No. 3,788,874 patent may be carried out. The teachings of the U.S. Pat. No. 3,788,874 patent are incorporated herein by reference.